This invention primarily concerns coffee bean roasting, although the invention can be applied to other roasting or heating applications as well.
The invention is directed to improvements on the coffee bean roasting apparatus and method described in U.S. Pat. No. 5,944,512, owned by the same assignee as this invention. U.S. Pat. No. 5,944,512 is hereby incorporated by reference in its entirety.
In the apparatus of U.S. Pat. No. 5,944,512, which was applicable to but not specific to coffee beans, coffee beans or other products were roasted in a chamber connected in a recirculating process stream loop with a cyclone separator which included a heating chamber. The patented machine had a gas flame or other heat source emanating from the bottom of the heating chamber and directed concentrically toward an incineration tube directly above. The process stream was introduced tangentially to the cyclone separator, via a circulating fan or blower within the process stream, and spiraled down to the lower region of the heating chamber, around the heating flame, then back upwardly inside a cylindrical shroud and just outside the incineration tube, then directed out of the cyclone separator and ducted back to the bean roasting chamber. By this design very little of the process stream co-mingled with the products of combustion from the heat source, and the process stream was heated to an effective temperature to roast the beans. In the cyclone separator, the chaff from the coffee beans was separated by centrifugal force, and settled down to a particle collection bin or hopper.
In the coffee bean roasters corresponding to U.S. Pat. No. 5,944,512 and sold by the assignee of the present invention, after a roast was completed the beans were released from the roasting chamber into a cooler, for cooling of the beans with ambient air drawn through the beans by a circulating blower. Smoke was released from the roasted beans into the ambient air, until the beans were cooled to a sufficient extent.
Also in the prior coffee bean roaster, a purge feature was included whereby, before the machine's heat source could be activated, safety concerns and regulations required that the entire system volume (atmosphere) be replaced by a volume of fresh air not less than five times the system volume, to prevent the possibility of ignition and explosion. A purge gate was included in a duct in the process stream, just downstream of an outlet of the cyclone separator. Prior to firing up the heating chamber each day, or after any involuntary shutdown, the purge gate would be opened to essentially close or throttle down the outlet from the process stream and to admit ambient air into the duct leading to the coffee bean roasting chamber. Thus, by means of the circulating fan downstream of the roasting chamber, ambient air was drawn into and through the entire system to purge potentially combustible (explosive) gases or particulates that may have accumulated, delivering the air and particulates into the cyclone separator and the heating chamber. These materials would be blown out through the incineration tube via the exhaust stack at its upper end, and the system would be purged and ready to be fired.
Although the patented coffee bean roasting system was mostly smokeless, at the end of the roast there was smoke in the roaster and the beans cooling in ambient air made more smoke. The smoke in the roaster primarily recirculated with the process stream, and the volume of smoke leaving the system through the incineration tube of the cyclone would be cleaned by incineration. The beans in the cooling tray would continue to generate smoke until falling below a certain temperature, and this typically happened about forty-five seconds after the beans were dumped into the cooler at the end of a roast. Other coffee roasters have used a similar arrangement for cooling the beans after the roast, in a cooling tray outside the roaster.